1. Field of the Invention
The present disclosure relates to an organic light emitting diode display device and, more particularly, to an organic light emitting diode display device including a cathode improved in transmittance and electrical property and a method of fabricating the same.
2. Discussion of the Related Art
Among various flat panel displays (FPDs), an organic light emitting diode (OLED) display device has superior properties such as high luminance and low driving voltage. The OLED display device includes an anode, an emitting layer and a cathode and a light is emitted due to an energy generated when an exciton by combination of a hole and an electron in the emitting layer transitions from an excited state to a ground state.
Since an additional light source is not necessary for the OLED display device of an emissive type, a thickness and a weight of the OLED display device are reduced. In addition, since the OLED display device has superior properties such as a low power consumption, a high brightness and a high response speed, the OLED display device is regarded as the next generation display device for portable electric devices.
The OLED display device may be classified into a top emission type and a bottom emission type according to a direction of light transmission. The bottom emission type OLED display device has advantages in stability and degree of freedom of fabrication. However, since the bottom emission type OLED display device has a limitation in aperture ratio, the bottom emission type OLED display device has disadvantages in application to a high resolution display device. Accordingly, the top emission type OLED display device has been widely researched.
In the top emission type OLED display device, a light of the emitting layer is emitted through a transparent cathode to display an image. In general, the cathode is formed of a metallic material including aluminum (Al). For example, the cathode may have a sheet resistance smaller than about 10Ω/□ and may have a relatively small thickness so that the light can be transmitted. However, when the cathode has a thickness of about 1000 Å to about 4000 Å for a sheet resistance smaller than about 10Ω/□, the cathode has a transmittance smaller than about 1% and the light is not transmitted through the cathode. In addition, when the cathode has a thickness of about 20 Å to about 200 Å for transmission of light, the cathode has a sheet resistance of about 100Ω/□ to about 10000Ω/□ and the OLED display device has non-uniformity in brightness due to voltage drop.
FIG. 1 is a graph showing transmittance with respect to wavelength for four thicknesses of a cathode of a light emitting diode display device according to the related art.
In FIG. 1, a cathode of aluminum having a thickness greater than about 300 Å has a relatively low transmittance of about 15% at a wavelength of about 550 nm and an emission efficiency of an OLED display device including the cathode is reduced.
After an anode is formed, a particle of an exterior may be strongly attached to the anode. Since the particle is not removed through a cleaning step before formation of an emitting layer, the cathode may directly contact the anode such that the anode and the cathode are electrically connected. As a result, a current from a driving thin film transistor (TFT) does not flow through the emitting layer. Instead, the current directly flows from the anode to the cathode and a light is not emitted from the emitting layer. Since the corresponding pixel region may become a dark pixel displaying a black color, a power consumption increases and a display quality is deteriorated.